# NTSB NYC84FA319: Sikorsky S-76A, N79K, Unionville, PA, September 22, 1984

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Field investigation · Final report
- Date: September 22, 1984, 11:30 local (15:30 UTC)
- Place: Unionville, PA
- Coordinates: 39.900253, -75.740417 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.9003&lon=-75.7404&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious, 5 minor, 8 uninjured; on the ground: 1 serious, 5 minor
- Status: Completed
- Report: Approved by Office Director
- Safety recommendations: Yes
- NTSB case key (mKey): 35370
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=NYC84FA319
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/35370/pdf
- Page: https://openairdocs.org/ntsb/NYC84FA319

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, approach - vfr pattern - final approach
  - engine installation,fire shield - chafed (contributing factor)
  - maintenance,design change - inadequate, manufacturer (cause)
  - maintenance,installation - improper, company maintenance personnel (cause)
  - rotor drive system,tail rotor drive shaft - chafed (contributing factor)
  - rotor drive system,tail rotor drive shaft - failure,total (cause)
- Loss of control - in flight, landing
  - directional control - not possible, pilot in command
- Hard landing, landing - flare/touchdown

## Analysis

ON APPROACH, ACFT YAWED RIGHT. PLT REDUCED POWER AND EXECUTED EMERG LNDG. BEFORE SHUTDOWN, IT WAS NOTED THE T/R WAS STATIONARY WHILE THE MAIN ROTOR CONTINUED TO TURN. INVESTIGATION REVEALED T/R DRIVE SHAFT HAD SEPARTED DUE TO THERMAL/MECHANICAL DAMAGE INCURRED BY CONTACT WITH ENGINE FIREWALL. FURTHER INVESTIGATION REVEALED THAT A FIREWALL MODIFICATION HAD BEEN DESIGNED WHICH INCLUDED A DOUBLER STRIP AT THE FWD AND AFT FIREWALL SECTION CONNECTION. PRESENCE OF DOUBLER WOULD DECREASE CLRNC BETWEEN FIREWALL AND T/R SHAFT. IT WAS FURTHER DETERMINED THAT, DURING INSTALLATION, THE FWD FIREWALL SECTION, TO WHICH THE DOUBLER IS ATTACHED, WAS MISPOSITIONED WITH RESULT THAT CLRNC WAS REDUCED TO NIL. COMPONENTS CAME INTO CONTACT DURING OPERATIONS.

## Aircraft

- Registration: [N79K](https://openairdocs.org/deregistered/N79K-1988-08-16), registration cancelled 1988-08-16, S/N 760098 (OpenAirDocs)
- Reported make and model: SIKORSKY S-76A
- Registry model: [Sikorsky S-76A](https://openairdocs.org/model/sikorsky-s-76a) (registry code 8143006) (OpenAirDocs)
- Category: Helicopter
- Serial number: 760098
- Airframe hours: 1786
- Engines: ALLISON A250C30S 650 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 135
- Registered owner: Keystone Helicopter Corp.
- Airworthiness certificate: Standard, Transport
- Last inspection: 100 hour, June 30, 1984, 100 hours before
- Departed: 40N, COATESVILLE, PA

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 39; airline transport, commercial; airplane ratings: single-engine land; instrument ratings: airplane, helicopter; medical: class 1, valid medical--no waivers/lim.; seat: right

## Weather

- Conditions: Visual (VMC), Day
- Wind: 160° at 3 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 70 °F, dew point 52 °F
- Altimeter: 30.00 inHg
- Observed at: PNE

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19840922076549A](https://openairdocs.org/incident/19840922076549A), Sep 22, 1984: Skrsky S76A, Unionville, PA, Substantial damage. Yaw began on short final, reduced power and hard landing made. Doubler strip broke and struck tail rotor driveshaft

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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